People diagnosed as having cancer are frequently treated with single or multiple cytotoxic chemotherapeutic agents (cytotoxic agents) to kill cancer cells at the primary tumor site or at distant sites to where cancer has metastasized. (U.S. Pat. No. 5,605,931 incorporated by reference herein in its entirety.) Chemotherapy treatment is given either in a single or in several large doses or, more commonly, it is given in small doses 1 to 4 times a day over variable times of weeks to months. There are many cytotoxic agents used to treat cancer, and their mechanisms of action are generally poorly understood.
Irrespective of the mechanism, useful chemotherapeutic agents are known to injure and kill cells of both tumors and normal tissues. The successful use of chemotherapeutic agents to treat cancer depends upon the differential killing effect of the agent on cancer cells compared to its side effects on critical normal tissues. Among these effects are the killing of hematopoietic blood forming cells, and the killing and suppression of the white blood cells, which can lead to infection. Acute and chronic bone marrow toxicities are also major limiting factors in the treatment of cancer. They are both related to a decrease in the number of hemopoietic cells (e.g., pluripotent stem cells and other progenitor cells) caused by both a lethal effect of cytotoxic agents or radiation on these cells, and via differentiation of stem cells provoked by a feed-back mechanism induced by the depletion of more mature marrow compartments. (U.S. Pat. No. 5,595,973 incorporated by reference herein in its entirety.) Stimulators and inhibitors of bone marrow kinetics play a prominent role in the induction of damage and recovery patterns (Tubiana, M., et al., Radiotherapy and Oncology 29:1, 1993).
Prevention of, or protection from, the side effects of chemotherapy would be a great benefit to cancer patients. The many previous efforts to reduce these side effects have been largely unsuccessful. For life-threatening side effects, efforts have concentrated on altering the dose and schedules of the chemotherapeutic agent to reduce the side effects. Other options are becoming available, such as the use of granulocyte, colony stimulating factor (G-CSF), granulocyte-macrophage-CSF (GM-CSF), epidermal growth factor (EGF), interleukin 11, erythropoietin, thrombopoietin, megakaryocyte development and growth factor, pixykines, stem cell factor, FLT-ligand, as well as interleukins 1, 3, 6, and 7, to increase the number of normal cells in various tissues before the start of chemotherapy (See Jimenez and Yunis, Cancer Research 52:413415; 1992). The mechanisms of protection by these factors, while not fully understood, are most likely associated with an increase in the number of normal critical target cells before treatment with cytotoxic agents, and not with increased survival of cells following chemotherapy.
Acute myelosuppression as a consequence of cytotoxic chemotherapy is well recognized as a dose-limiting factor in cancer treatment. (U.S. Pat. No. 5,595,973) Although other normal tissues may be adversely affected, bone marrow is particularly sensitive to the proliferation-specific treatment such as chemotherapy or radiotherapy. For some cancer patients, hematopoietic toxicity frequently limits the opportunity for chemotherapy dose escalation. Repeated or high dose cycles of chemotherapy may be responsible for severe stem cell depletion leading to serious long-term hematopoietic sequelea and marrow exhaustion.
Despite advances in the field of chemotherapy, prior art methods have proven to be of limited utility in minimizing chemotherapy-induced depletion of hematopoietic stem cells and their progeny. Thus, there is a need for improved therapeutic methods and pharmaceutical compositions for increasing hematopoietic cell survival following chemotherapeutic treatments, as well as for decreasing the adverse effects of chemotherapy on the bone marrow.